Frequency of Maxillary Sinus Mucous Retention Cysts in a Central Brazilian Population.

STATEMENT OF THE PROBLEM
Mucous retention cysts (MRCs) of the maxillary sinus are lesions with undefined pathogenesis. In recent researches, geographical and climatic aspects have been related as risk factors.


PURPOSE
The purpose of this study was to determine the frequency of MRCs of the maxillary sinus using panoramic radiographs.


MATERIALS AND METHOD
A total of 631 panoramic radiographs were selected from a secondary database from a private radiology clinic and analyzed by two specialists in dental radiology according to gender, age, month, relative air humidity, and mean temperature.


RESULTS
A total of 87 (6.89%) radiographic images were suggestive of MRCs. Thirty-five MRCs (40.22%) were detected on the right side, 10 (11.49%) on the left side and 42 (48.29%) on both sides. A high frequency was detected in female participants (n=45; 51, 72%), those aged 18-35 years (n=31; 35, 63%) and those from August (n=24; 27.59%) and July (n=22; 25.29%).


CONCLUSION
The frequency of MRCs was low, and no statistically significant correlation was found between the prevalence of MRCs and the studied variables with the exception of the mean temperature.


Introduction
Maxillary sinuses, also known as paranasal sinuses, are described as pneumatic (air-filled) cavities. [1] In humans; they are restricted to the skull and can host cystic, inflammatory or neoplastic lesions. [2] Mucous retention cysts (MRCs) of the maxillary sinus are asymptomatic lesions that are characterized by retention of mucus from the mucous glands of the epithelial lining of the maxillary sinus. [3][4] MRCs are the most frequent lesion of the maxillary sinus [2,[4][5][6][7] and affect patients of all races, both genders and various age groups. [3][4][7][8][9][10] The pathogenesis of MRCs is undefined, [3,[9][10] although it is strongly related to allergic, inflammatory and infectious processes, trauma, relative humidity and room temperature. [3][4][8][9][10][11][12] Radiographically, MRCs appear as rounded, radiopaque, well-defined images varying in size and located within the maxillary sinus [3,8].MRCs may be unilateral or bilateral, [12][13] and they commonly emanate from the sinus floor. [2] MRCs have been studied in different populations [3, 7-8, 11, 14-15] using different methodologies, including analysis during surgical procedures, [13] panoramic radiographs, [3,9,12] computed tomograp- is extremely well suited for imaging findings in the floor or posterior wall of the maxillary sinus. [4,18] There is limited information on the occurrence of maxillary sinus abnormalities in the Brazilian population. [7,12,16] The geographical and climatic specificities and differences justify the analysis of the frequency of MRCs of the maxillary sinus in the population of Central Brazil, which was performed using panoramic radiographs.    Table 1 shows the distribution of MRCs as a function of gender, age and affected side. there was a significant correlation only between the frequency of MRCs and the mean temperature. Figure   1 shows examples of panoramic radiographs of patients with unilateral and bilateral MRCs.

Discussion
MRCs are defined as mucoid-filled cysts that develop when the seromucous glands of the mucosa of the maxillary sinus become obstructed. [3] MRCs are usually asymptomatic, seldom require treatment and are diagnosed with routine radiographic examinations. Regarding gender, MRCs were slightly more frequently found in females than in males (1.08:1).
This finding contrasts with the data reported by other authors, [7-9, 11, 19] who identified a higher frequency of MRCs among the male population. However, Bhattacharyya [5] observed a female-male ratio of 2.4:1 when determining the incidence of MRCs in a population undergoing evaluation for chronic rhinosinusitis. This study was conducted in a private radiolo-gy clinic, and the panoramic exams were undertaken for different diagnoses purposes, such as surgical planning, oral disease diagnosis, and orthodontic diagnosis. The higher frequency of MRCs among women observed in this analysis may be associated with more women than men being referred to the diagnostic imaging service and may not be a true predilection.
In the present study, the age of the patients with radiographic images indicating MRCs ranged from 3 to 88 years, and a high number of MRCs was observed in participants in the 18-35 year age group (31/87).
Although several studies suggest that MRCs are found in the greatest proportion in second and third decades of life, [3,[7][8][9]  can promote an inflammatory response in the respiratory tract, which can cause increased production of acidity, viscosity and consistency of the mucus produced by the airways, leading consequently to a decrease response and / or efficacy of the mucociliary system. [23] It is important to note that Brazil is a tropical country, and in most regions, there are no drastic temperature changes during the year. In this climate, the four seasons are not well defined, and therefore, comparisons between studies conducted in different geographical areas of Brazil and between studies conducted in other countries should be made with caution.
Investigations using other imaging methods, such as cone beam computed tomography, with a greater number of participants should be performed to establish three-dimensional correlations.

Conclusion
The frequency of MRCs of the maxillary sinus was low (6.89%). Females and those aged 18-35 years were the groups with the greatest numbers of cases.
The peak frequency was in August, and the lowest was in February. Statistical analyses revealed a correlation between the frequency of MRCs and the mean temperature.